Search

A systematic study of the X2Aun(X = La, Y, Sc;n= 1–9) clusters are performed by using the density functional theory at TPSS level. The structures, stabilities, electronic, and magnetic properties are investigated in comparison with pure gold clusters. The results show that the transition points of the doped clusters from two-dimensional to three-dimensional structure are obviously earlier than gold clusters. The impurity X atoms tend to occupy the most highly coordinated position and form the largest probable number of bonds with gold atoms. In addition, the impurity atoms can strongly enhance the stabilities of gold clusters. It indicates that the impurity atoms dramatically affect the geometries and stabilities of the Aunclusters. The highest occupied molecular orbital–lowest occupied molecular orbital gap, vertical ionisation potential, and chemical hardness show that the X2Au6clusters have higher stabilities than the others. In La2Au1–9, Y2Au1–7, and Sc2Au1–4clusters, the charges transfer from X atoms to the Aunframes. The total magnetic moments of X2Aunclusters exist distinctly odd–even alternation behaviours except for La2Au4and Sc2Au4clusters. [ABSTRACT FROM AUTHOR]

The fumigant action of four plant oils viz., garlic (Allium sutivumL.), clove [Syzygium aromaticum(L.) Merr. & Perry], attarasa [Litsea cubeba(Lour.) Pers.] and coriander (Coriandrum sativumL.) oils, was tested against eggs ofCallosobruchus chinensis(L.). After 72 h of exposure, garlic oil exhibited the highest fumigant toxicity against eggs ofC.chinensis, which was followed by clove, attarasa and coriander oils, with LC50values of 0.34, 1.12, 3.78 and 5.29 μL/L air, respectively. Binary mixtures of clove/coriander oil and clove/attarasa oil showed significant synergism with the co-toxicity factor of 241.77 and 114.15, respectively, while other combinations did not show any synergism. Optimal volume proportions of these synergistic combinations were 24:76 for clove/coriander oil and 41:59 for clove/attarasa oil, which were screened out with the toxicity index and were further confirmed by the co-toxicity coefficient. GC-MS analysis of these oils showed that eugenol, aceteugenol and β-caryophyllene were major components of clove oil, linalool, α-pinene, camphor, geranyl acetate and γ-terpinolene of coriander oil, α-citral, β-citral, D-limonene, linalool and sulcatone of attarasa oil, and sulphur compounds of garlic oil. Based on high toxicity againstC.chinensiseggs and synergistic action of plant oil mixtures, clove oil can be used as another potential grain fumigant for the management of stored legume pests. [ABSTRACT FROM AUTHOR]

Density functional theory has been applied to study the geometric structures, relative stabilities, and electronic properties of cationic [AunRb]+and Aun+1+(n= 1–10) clusters. For the lowest energy structures of [AunRb]+clusters, the planar to three-dimensional transformation is found to occur at cluster sizen= 4 and the Rb atoms prefer being located at the most highly coordinated position. The trends of the averaged atomic binding energies, fragmentation energies, second-order difference of energies, and energy gaps show pronounced even–odd alternations. It indicated that the clusters containing odd number of atoms maintain greater stability than the clusters in the vicinity. In particular, the [Au6Rb]+clusters are the most stable isomer for [AunRb]+clusters in the region ofn= 1–10. The charges in [AunRb]+clusters transfer from the Rb atoms to Aunhost. Density of states revealed that the Au-5d, Au-5p, and Rb-4p orbitals hardly participated in bonding. In addition, it is found that the most favourable channel of the [AunRb]+clusters is Rb+cation ejection. The electronic localisation function (ELF) analysis of the [AunRb]+clusters shown that strong interactions are not revealed in this study. [ABSTRACT FROM AUTHOR]

The geometric structures, stabilities, and electronic properties of small size anionic [AunRb]−and Aun+1−(n= 1–10) clusters have been systematically investigated by using density functional theory. The optimised geometries show that the structures of [AunRb]−clusters favour the three-dimensional structure atn≥ 8. The Rb atoms tend to occupy the most highly coordinated position and form the largest probable number of bonds with gold atoms. One Au atom capped on [Aun-1Rb]−structures is the dominant growth pattern forn= 2–8 and Rb atom capped on Aun−structures forn= 9–10. The averaged atomic bonding energies, fragmentation energies, second-order difference of energies, and highest occupied molecular orbital–lowest unoccupied molecular orbital gaps exhibit a pronounced even–odd alternations phenomenon. The charges in [AunRb]−clusters transfer from the Rb atoms to Aunhost. In addition, it is found that the most favourable dissociation channel of the [AunRb]−clusters is to eject a Rb atom and the highest energy dissociation path is Rb−anion ejection. [ABSTRACT FROM PUBLISHER]

The equilibrium geometric structures, stabilities and electronic properties of Si2Agn(n= 1–8) and pure silver Agn(n≤ 10) clusters have been systematically investigated by using meta-generalised gradient approximation. Due tosp3hybridisation, the lowest energy structures of Si2Agnclusters forn> 2 favour the three-dimensional structure. The silicon atoms prefer to be located at the surface of the host silver clusters. By analysing the relative stabilities, it is found that the di-bridged structure Si2Ag2isomer is the most stable structure for Si2Agn(n= 1–8) clusters. The highest occupied–lowest unoccupied molecular orbital gaps, exhibiting a pronounced even–odd alternation, indicate that the doped clusters with even number of atoms have enhanced chemical stability than those with odd number of atoms. The results of Wiberg bond indices and electronic localisation function show that the stronger Si–Si and Si–Ag interaction may be the main driving force for the higher stability of Si2Agnclusters. [ABSTRACT FROM AUTHOR]

In this paper, we develop a complete energy matrices approach investigating the defect structure and EPR parameters ( , , and ) for Er3+ in molybdates. In this approach, the crystal-field parameters used in the calculations are determined from the superposition model and the structural data for tetragonal distortion. The local distortion angles Δθ = −1.628°, Δθ = −1.843° and Δθ = −2.874° are obtained for Er3+ in SrMoO4, PbMoO4 and CaMoO4 crystals, respectively. Moreover, the influence of the orbital reduction factor k and the local distortion angle Δθ on the EPR parameters is analyzed. [ABSTRACT FROM PUBLISHER]

Ab initio method based on density functional theory at PW91PW91 level has been applied in studying the geometrical structures, relative stabilities, and electronic properties of small bimetallic AuBe ( n = 1-8) cluster cations. The geometrical optimizations indicate that a transition point from preferentially planar (two-dimensional) to three-dimensional (3D) structures occurs at n = 6. The relative stabilities of AuBe clusters for the ground-state structures are analyzed based on the averaged binding energies, fragmentation energies, and second-order difference of energies. The calculated results reveal that the AuBe and AuBe clusters possess higher relative stability for small size AuBe ( n = 1-8) clusters. The HOMO-LUMO energy gaps as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. Sequently, the natural population analysis and polarizability for our systems have been analyzed and compared further. [ABSTRACT FROM AUTHOR]

The equilibrium geometries, relative stabilities, and electronic properties of MnAgm (M=Na, Li; n + m ≤ 7)as well as pure Agn, Nan, Lin (n ≤ 7) clusters are systematically investigated by means of the density functional theory. The optimized geometries reveal that for 2 ≤ n ≤ 7, there are significant similarities in geometry among pure Agn, Nan, and Lin clusters, and the transitions from planar to three-dimensional configurations occur at n = 7, 7, and 6, respectively. In contrast, the first three-dimensional (3D) structures are observed at n + m = 5 for both NanAgm and LinAgm clusters. When n + m ≥ 5, a striking feature is that the trigonal bipyramid becomes the main subunit of LinAgm. Furthermore, dramatic odd-even alternative behaviours are obtained in the fragmentation energies, secondorder difference energies, highest occupied and lowest unoccupied molecular orbital energy gaps, and chemical hardness for both pure and doped clusters. The analytic results exhibit that clusters with an even electronic configuration (2, 4, 6) possess the weakest chemical reactivity and more enhanced stability. [ABSTRACT FROM AUTHOR]

Using the meta-generalized gradient approximation (meta-GGA) exchange correlation TPSS functional, the geometric structures, the relative stabilities, and the electronic properties of bimetallic AgnX (X=Au, Cu; n=1-8) clusters are systematically investigated and compared with those of pure silver clusters. The optimized structures show that the transition point from preferentially planar to three-dimensional structure occurs at n = 6 for the AgnAu clusters, and at n = 5 for AgnCu clusters. For different-sized AgnX clusters, one X (X=Au or Cu) atom substituted Agn+1 structure is a dominant growth pattern. The calculated fragmentation energies, second-order differences in energies, and the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps show interesting odd-even oscillation behaviours, indicating that Ag2;4;6;8 and Ag1;3;5;7X (X=Au, Cu) clusters keep high stabilities in comparison with their neighbouring clusters. The natural population analysis reveals that the charges transfer from the Agn host to the impurity atom except for the Ag2Cu cluster. Moreover, vertical ionization potential (VIP), vertical electronic affinity (VEA), and chemical hardness (η) are discussed and compared in depth. The same odd-even oscillations are found for the VIP and of the AgnX (X=Au, Cu; n=1-8) clusters. [ABSTRACT FROM AUTHOR]

Ab initio methods based on density functional theory at BP86 level were applied to the study of the geometrical structures, relative stabilities, and electronic properties of small bimetallic BeAu ( n = 1-9) clusters. The optimized geometries reveal that the most stable isomers have 3D structures at n = 3, 5, 7, 8, and 9. Here, the relative stabilities were investigated in terms of the averaged atomic binding energies, fragmentation energies and second-order difference of energies. The results show that the planar BeAu structure is the most stable structure for BeAu clusters. The HOMO−LUMO gap, vertical ionization potential, vertical electron affinity and chemical hardness exhibit a pronounced even-odd alternating phenomenon. In addition, charge transfer and natural electron configuration were analyzed and compared. [ABSTRACT FROM AUTHOR]

A systematic study on the geometric structures, relative stabilities, and electronic properties of small bimetallic AuNa ( n = 1-9) clusters has been performed by means of first-principle density functional theory calculations at the PW91PW91 level. The results show that the optimized ground-state isomers adopt planar structures up to n = 5, and the Na-capped geometries are dominant growth patterns for n = 6-9. Dramatic odd-even alternative behaviors are obtained in the second-order difference of energies, fragmentation energies, highest occupied-lowest unoccupied molecular orbital energy gaps, and chemical hardness for both AuNa and Au clusters. It is found that AuNa and Au have the most enhanced stability. Here, the size evolutions of the theoretical ionization potentials are in agreement with available experimental data, suggesting a good prediction of the lowest energy structures in the present study. In addition, the charge transfer has been analyzed on the basis of natural population analysis. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of silver-doped gold clusters AunAgv (2 ≤ n ≤ 10; v = 0, ±1) have been systematically investigated using density functional theory. The results show that the ground state optimal structures of the cationic and neutral clusters are found to be planar up to n = 3 and 9, respectively. However, for the anionic clusters, no three-dimensional lowest-energy structures are obtained according to DFT calculations. The calculated binding energy and dissociation energy as a function of cluster size exhibit odd-even alternations. The natural population analysis indicates that in AunAgv clusters charges transfer from the Ag atom to the Au frames. The trends for the vertical detachment energies, adiabatic electron affinities, adiabatic ionization potentials, and chemical hardness of AunAgv clusters, as the cluster size increases, are studied in detail and compared with the available experimental data. [ABSTRACT FROM AUTHOR]

The geometric structures, relative stabilities, and electronic properties of a series of tetra-aluminum oxide clusters, [image omitted] ( [image omitted], [image omitted]), were systematically investigated using density functional theory calculations at the B3LYP level. The optimized geometries reveal a structural transition from a two-dimensional to a three-dimensional structure for n ≤5 for the neutral species, but the three-dimensional structures are preferable for all negative clusters with the exception of [image omitted]. The dissociation energy, the second difference energy and the highest occupied-lowest unoccupied molecular orbital gaps as a function of the cluster size exhibit a significant even-odd alternation phenomenon. It is found that the neutral [image omitted] cluster is relatively stable and exhibits strong chemical stability. Furthermore, the calculated (vertical and adiabatic) electron detachment energies are also compared with previous experimental data obtained from photoelectron spectra. [ABSTRACT FROM AUTHOR]

Abstract: The geometrical structures, relative stabilities, and electronic properties of bimetallic Au n Mg () clusters have been systematically investigated by means of first-principle density functional theory. The results show that the ground-state isomers have planar structures for . Here, the calculated fragmentation energies, the second-order difference of energies, the highest occupied–lowest unoccupied molecular orbital energy gaps, and the hardness exhibit a pronounced odd–even alternation, manifesting that the clusters, especially Au2Mg, with even-number gold atoms have a higher relative stability. On the basis of natural population analysis, the charge transfer and magnetic moment are also discussed. [Copyright &y& Elsevier]